Chemical vapor deposition (CVD) processes use induced chemical reactions of gaseous precursor molecules to deposit one or more thin-film layers onto the surface of a substrate. For example, a trimethylgallium and arsine reaction induced by a combination of elevated temperature and radio frequency energy can be used to produce a gallium arsenide film layer. A wide variety of CVD precursor substances are known.
Frequently encountered challenges involving CVD reactors include uniformity of deposition, contamination issues, and downtime for reactor maintenance affecting throughput. Uniformity of deposition requires a corresponding uniformity of reactor environment conditions in the vicinity of substrate surface being processed, including uniform reaction gas mixture and concentration and uniform temperature. Ideally, deposition will occur only on the surface of the substrate being processed, with such deposition being substantially uniform over that substrate. In practice, unwanted deposition (as well as precursor condensation) may occur also on some surfaces of the reactor itself that are exposed to the precursor molecules or intermediate reaction products under conditions that allow deposition. When surface deposits build up in the reactor, material can break off to introduce contaminant particles to the reactor environment. The surface build-up can also adversely affect processing conditions that may lead to decreased deposition rates onto the substrate or deposition non-uniformity. To handle these issues, the reactor must be periodically cleaned to remove any unwanted depositions from the reactor surfaces, which leads in turn to reactor downtime and reduced throughput.